Many fibers are prepared from a solution of the polymer in a solvent (called the “polymer dope”) by extruding or spinning the polymer dope through a die or spinneret to prepare or spin a dope filament. The solvent is subsequently removed to provide the fiber or yarn. In the preparation of certain fibers, the solvent utilized is a solvent acid, such as polyphosphoric acid (PPA). Unlike many typical solvents, PPA removal is generally more difficult, in part due to its polymeric nature. Incorporation of heteroatoms into the polymer may also act to inhibit removal of polyphosphoric acid from the fiber or yarn. Existing processes for removal of polymeric PPA solvent from a polymeric material typically require long washing times or elevated leaching temperatures if a substantial amount of PPA is to be removed.
For example, Sen et al., U.S. Pat. No. 5,393,478, discloses a process for leaching polyphosphoric acid from the polybenzazole dope filament by contacting with a leaching fluid at a temperature of at least about 60° C.
Sen et al., U.S. Pat. No. 5,525,638, discloses a process for washing polyphosphoric acid from the polybenzazole dope filament by using multiple washes, typically at about room temperature, slowly reducing phosphorous concentration from the spun fiber, allegedly to improve the physical properties of the resultant polymeric fiber.
Further improvements in the physical properties of and/or removal of phosphorous from fibers spun from polyphosphoric acid are needed. These and other objects of the invention will become more apparent from the present specification and claims.
The present invention is directed, in part, to processes for hydrolyzing polyphosphoric acid in a never-dried spun multifilament yarn, comprising removing surface liquid from filaments in a never-dried spun multifilament yarn; and contacting the yarn with a hot surface to hydrolyze polyphosphoric acid, wherein the filaments remain substantially unfused.
The present invention is also directed, in part, to processes for removing the residual polyphosphoric acid from a multifilament yarn, comprising spinning a bundle of filaments from a solution comprising polyareneazole polymer and polyphosphoric acid into a coagulation bath; removing the bundle of filaments from the bath in the form of a multifilament yarn; removing surface liquid from the filaments in the yarn; contacting the yarn with a hot surface to hydrolyze polyphosphoric acid; and removing hydrolyzed polyphosphoric acid from the yarn, wherein the filaments remain substantially unfused.
The invention is also directed, in part, to processes for hydrolyzing polyphosphoric acid in a never-dried filament comprising polyareneazole and polyphosphoric acid, the process comprising removing surface liquid from the filament, and contacting the filament with a hot surface to hydrolyze polyphosphoric acid.
The invention is further directed, in part, to processes for hydrolyzing polyphosphoric acid in a shaped article comprising polyareneazole polymer and polyphosphoric acid, the process comprising removing surface liquid from the shaped article; and contacting the shaped article with a hot surface to hydrolyze polyphosphoric acid.